The present invention relates to a display panel and a method for fabricating the display panel. The display panel of this invention is applicable to a liquid crystal panel, a plasma display panel, an electrochromic display panel and the like.
In order to reduce the thickness of a liquid crystal panel, that is, one of display devices, reduction in the thickness of a substrate has been conventionally examined. In a current liquid crystal panel, a pair of glass substrates each having a thickness of 3 mm through 0.4 mm are generally used, and a liquid crystal layer with a thickness of several μm is interposed between these substrates. When a glass substrate with a thickness smaller than 0.4 mm is used, the mechanical strength is lowered, and hence, there arises, for example, a problem that the glass substrate is broken during the use.
Japanese Laid-Open Patent Publication No. 6-340029 discloses a layered plate in which a glass film with a thickness of 500 μm or less is provided on one face or both faces of a resin plate composed of at least one resin layer. This layered plate has surface hardness equivalent to that of glass and a thermal characteristic and a cut characteristic of the resin as well as surface characteristics such as solvent resistance and an anti-static property equivalent to those of glass.
Japanese Laid-Open Patent Publication No. 2001-113631 discloses a plastic/glass film layered product in which a plastic film with a thickness not less than 1 μm and not more than 1000 μm is provided and fixed on at least one face of a glass film with a thickness not less than 0.1 μm and not more than 100 μm. This layered product has chemical resistance, abrasive resistance and a gas barrier property equivalent to those of glass and is good at a handling property and a fabrication quality.
Japanese Laid-Open Patent Publication No. 2001-162721 discloses a heat-curing type resin composite in which a covering layer of a glass film or a combination of a glass film and a resin layer is fixed on a face of a heat-curing type resin body. Also, it is described in Paragraph 0041 of this publication that the glass film has a thickness of preferably 0.1 through 100 μm and more preferably 0.1 through 20 μm.
None of the aforementioned publications discloses use of the layered product or the composite described therein as a substrate for a display device. The present inventors have fabricated liquid crystal panels by using these layered product and the composite and using a fabrication line for liquid crystal panels, resulting finding the following:
First, in order that a liquid crystal panel resists impact applied on the fabrication line, both faces of a glass substrate should be coated with a resin. Accordingly, the total thickness of the layered product or the composite is increased, and hence, it is difficult to reduce the thickness and the weight of a display device. In addition, the fabrication cost is increased.
Secondly, since the heat resistance temperature is varied (approximately between 250° C. through 300° C.) depending upon the kind of resin to be employed, the quantity of heat appliable to the layered product or the composite during the fabrication process is restricted. Also, in placing a resin layer on a glass substrate and in heating/cooling process for the layered plate, a warp is caused in the layered product or the composite due to the difference in the coefficient of thermal expansion between the glass and the resin, and hence, the ratio of defectives is high. For example, in the case where a layered substrate in which a resin layer is provided on a glass substrate with a thickness of approximately 0.2 mm is allowed to pass through the fabrication line, when the heating/cooling process is repeated, a warp is caused in the substrate due to the difference in the coefficient of thermal expansion between the glass and the resin even at a temperature lower than the heat resistance temperature of the resin. As a result, a problem may occur that the substrate is broken or the patterning accuracy or the aligning accuracy is lowered. Accordingly, due to these restrictions on the fabrication line, the layered product and the composite disclosed in the aforementioned publications cannot be suitably used for mass production of liquid crystal panels.
On the other hand, Japanese Laid-Open Publication No. 2002-297054 discloses a substrate for a display device using a layered sheet including a glass layer with a thickness of 50 through 700 μm and resin layers, each with a thickness of 1 through 7000 μm and a given average coefficient of linear thermal expansion, on both faces of the glass layer. According to the substrate for a display device disclosed in this publication, since the difference in the average coefficient of linear thermal expansion between the glass layer and the resin layers is small, change such as a crack is not observed in the resin layers in a heat resistance evaluation test. In this substrate for a display device, however, since the resin layers are formed on the faces of the glass layer, when a pair of these substrates for a display device are used for fabricating a liquid crystal panel, the thickness of the liquid crystal panel is large. Thus, it is difficult to reduce the thickness and the weight of the display panel.